1. Field of the Invention
The present invention relates to an optical disk, an optical disk device, and an optical disk recording method. The present invention is applied to, for example, a compact disk. By correcting the timing of a modulation signal according to a change pattern of a modulation signal, a jitter at the time of reproduction is reduced and recorded data can be surely reproduced.
2. Description of the Related Art
In a conventional compact disk, data to be recorded are subjected to data processing and thereafter subjected to an EFM (Eight-to-Fourteen Modulation) modulation. For a predetermined fundamental period T, a pit sequence having a period in the range of 3T to 11T is thereby formed. Thereby, audio data or the like, for example, are recorded.
Corresponding to this, a compact disk player irradiates a laser beam on the compact disk and receives a returned light therefrom. The compact disk player thus obtains a reproduced signal having a signal level changed according to the light quantity of the returned light, converts this reproduced signal to a binary value by using a predetermined slice level, and thus generates a binary signal. Furthermore, the compact disk player drives a PLL circuit in response to this binary signal to generate a reproduction clock and latches binary signals successively by using the reproduction clock. Thereby, the compact disk player generates reproduced data having a period in the range of 3T to 11T and corresponding to the pit sequence formed on the compact disk.
The compact disk player conducts data processing corresponding to the data processing conducted at the time of recording, on the reproduced data thus generated. In this way, the compact disk player reproduces audio data or the like recorded on the compact disk.
By the way, in the conventional compact disk player, a jitter is contained in the reproduced signal. It may be considered that this jitter occurs by various causes such as a noise of a laser beam used for readout, a thermal noise of an electric system, a disk noise or the like. The jitter reduces the phase margin of the reproduced signal. In an extreme case, the jitter makes it difficult to reproduce data correctly.
However, this jitter is essentially due to an inter-symbol interference caused by preceding and succeeding pits (Shigeo Kubota, "Aplanatic condition required to reproduce jitter-free signals in an optical digital disk system", App. Optics 1987, Vol. 26, No. 18, pp. 3961-3970). The jitter changes according to the land and pit located before and behind the laser beam radiation position.